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The curve at Lake Shore Drive and Oak Street in Chicago is a favorite nudge. The tight turn makes it one of the city’s most dangerous curves. To try and limit wrecks, in September 2006 the city painted a series of white lines perpendicular to traveling cars. The lines get progressively narrower as drivers approach the sharpest point of the curve, giving them the illusion of speeding up, and nudging them to tap their brakes.

Exactly how effective have these lines been in preventing crashes? Until now, only anecdotal accounts have been available. What about a little hard data? According to an analysis conducted by city traffic engineers, there were 36 percent fewer crashes in the six months after the lines were painted compared to the same 6-month period the year before (September 2006 – March 2007 and September 2005 – March 2006).

To see if it could make the road even safer, the city installed a series of overhead flashing beacons, yellow and black chevron alignment signs, and warning signs posting the reduced advisory speed limit. Again, accidents fell – 47 percent over a 6-month period (March 2007 – August 2007 and March 2006 – August 2006). Keep in mind that the post-six-month period effect included both the signs and the lines.

How much more these calming signals will affect driving is unknown, but the city considers the numbers a sign of success. A drive between the North and South Sides is now safer and quicker for everyone.

Hat tip: Chicago Department of Transportation for providing its data.

Addendum: A video simulating the Lake Shore Drive effect can be found on the original amazon page for the hardcover edition of Nudge. Scroll down the page to see the “related media.” The Lake Shore Drive effect is in the second video, titled “Richard Thaler Explains the Nature of Nudges.” The key footage is about halfway through.

In Nudge, Thaler and Sunstein talk about a curve in Chicago’s Lake Shore Drive that uses a nice visual illusion to nudge drivers to slow down. Road planners in Philadelphia have been experimenting with painted illusions of speed bumps on some roads to accomplish a similar effect. From the New York Times:

The triangles are known variously as 3-D, virtual or just plain fake speed humps. They are among the latest tools in the age-old battle between drivers who exceed speed limits in residential neighborhoods and residents, law enforcement officers and government officials who want to slow them down.

Real speed humps — not to be confused with their more jarring cousins, speed bumps, a mainstay of some parking lots — are rounded mounds of traffic-calming asphalt that generally span a roadway. The virtual variety — flat pieces of plastic that are burned into the street, with the configuration of the colored lines conveying the illusion that a driver is about to cross the real thing — is less expensive ($500 each, versus $2,000), does not impede water flow and poses no threat to ambulances or other speeding emergency vehicles.

City road crews burned 10 sets of the humps into a half-mile stretch of road to tests their effects on drivers.

Before installation, Ms. Tolson said, drivers along that stretch of the two-lane road, often used as a neighborhood shortcut, were clocked averaging 38 miles per hour, 13 m.p.h. above the posted speed limit. A month later, that figure has dropped to 23 m.p.h.

Addendum: Tom Vanderbilt of How We Drive has similar thoughts to Colin. Check out Vanderbilt’s post for a bird’s eye shot of the Lake Shore Drive curve.

One of the main drawbacks is that people who live in the neighborhood or use the road regularly (and remember most crashes happen close to our homes) will become familiar with the visually confusing speed bumps. There’s other ways to tackle the problem, however. The road could be narrowed — a proven speed reducer — or, similarly, parking permitted on both sides (it’s unclear from the photo whether that’s the case). Different types of pavement treatments could be installed to break up the visual notion of the road as a straightaway. Most ambitiously, the yellow line could be removed. A number of studies have shown that, in the absence of a dividing line, speeds decrease, while distance between opposing traffic streams actually grows. The yellow line is a subtle signal to speed up — one’s territory is “safely” marked. Whether removing the line is more or less “safe” is a relative question; after all, the best safety measure for all involved, drivers and neighborhood residents, would be lower speeds.

The University of Chicago has put together two Nudge videos starring Richard Thaler, Cass Sunstein, and the Hyde Park dining institution known as Noodles (with cameos by Lake Shore Drive, the Graduate School of Business Cafeteria, and Clocky).

Thaler and Sunstein reminisced at their favorite Hyde Park lunch spot, Noodles, where they say they did some of their best work on the book. Noodles was so important to the creative process, it even made the acknowledgments. The two talk about what each brought to the project, the origin of the elephants on the book cover, their fear of forms, and their hopes for a new political consensus in the country.

About

The Nudge blog is the online companion to Richard Thaler and Cass Sunstein’s “Nudge: Improving Decisions About Health, Wealth, and Happiness.” Here you’ll find much more about nudging, choice architecture, libertarian paternalism, and many other terms you won’t read about in standard economics books.

Cass Sunstein is currently the Administrator of the White House Office of Information and Regulatory Affairs and has no affiliation with the Nudge blog.

The Nudge blog is edited by John Balz.

Tell us about a nudge

The possibilities for great nudges are everywhere. For a list of favorites from the book, check out our dozen nudges. We invite readers to send their own nudge suggestions to nudgeblog@gmail.com.

What is Choice Architecture?

Decision makers do not make choices in a vacuum. They make them in an environment where many features, noticed and unnoticed, can influence their decisions. The person who creates that environment is, in our terminology, a choice architect. The goal of Nudge is to show how choice architecture can be used to help nudge people to make better choices (as judged by themselves) without forcing certain outcomes upon anyone, a philosophy we call libertarian paternalism. The tools highlighted are: defaults, expecting error, understanding mappings, giving feedback, structuring complex choices, and creating incentives.

For a user-friendly introduction to choice architecture, check out this paper.